Hydroconversion processes for the upgrading of heavy cretaceous crude oils, bitumens and heavy residues are well known. Upgrading processes are conducted to remove or reduce contaminants in the oil and to convert the heavier components of the oil into lower boiling point hydrocarbon products.
The hydroconversion process is normally conducted in a fixed bed or an ebullated bed reactor. In an ebullated bed reactor the catalyst is ebullated by the liquid and ga thereby expanding the bed to a predetermined level. This near perfect mixing provides better contact between the liquid and gaseous phases and the catalyst. In a fixed bed system a catalyst bed is provided within the reaction zone of the reactor. The method of packing the bed, particle size and bed porosity are determined by the nature of the reactor, and the liquid hourly space velocity. The heavy oil feedstock is reacted with hydrogen at high temperatures.
A heterogeneous catalyst is usually utilized in a commercial hydroconversion process to improve product yield and quality. Exemplary catalysts would include molybdenum, cobalt or nickel deposited on an alumina substrate. However, during the hydroconversion process coke formation will take place. The coke, together with certain metals, (hereinafter collectively referred to as a catalytic poisoning agent), will deposit on the catalyst pellet surface. It has been observed that the coke and metal deposition generally takes place on the catalyst surface, thereby progressively decreasing the active surface area and pore volume thereof. The decrease in catalytic activity thus follows a time activity curve.
Once the catalyst has become deactivated, the methods whereby the poisoned catalyst was replaced are as follows. In the case of a fixed bed reactor system, the reactor is shut down and the catalyst is replaced with new or regenerated catalyst. Alternatively, in the case of an ebullated bed reactor, the catalyst is replaced by continuous addition of fresh catalyst and simultaneous removal of poisoned catalyst These above-described methods are those in current commercial usage. It is to be noted that both reactor shut-downs and catalyst replacement are very costly. Therefore, one continually seeks to prolong the effective life-time of the catalyst.
In Canadian Pat. No. 1,073,389, a process is described for suppressing the deposition of coke on the reactor walls. Coal particles are slurried with the feed and the slurry introduced into an open tube reactor. A catalyst is not utilized.
Ranganathan et. al. in Canadian Pat. No. 1,094,492, teaches a process for preventing carbonaceous deposits in the reaction zone. An iron-coal catalyst is admixed with the feed. An open-tube reactor was used.
It is also known, as disclosed in Canadian Pat. No. 1,117,887 issued to Patmore et. al., that in a particular thermal hydrocracking process the formation and deposition of coke and solids in the reactor poses a major problem. More specifically, the thermal hydrocracking process involves pumping hydrogen and a heavy oil feedstock hydrogenate and/or hydrocrack the feedstock. Reaction pressures of up to 3500 psig and temperatures of up to 500.degree. C. may be utilized. Patmore et. al. discovered that for such a process, the problems of coke deposits forming in the reactor could be overcome by mixing an active catalyst with the feedstock. The catalyst comprised a finely divided carbonaceous material carrying a Group VIA or VIII metal. The heavy oil feedstock and catalyst slurry were passed into an open tubular reactor in the presence of hydrogen and, following reaction, the mixed effluent and catalyst were removed from the hydrocracking zone and treated further.
German Pat. No. 933,648, discloses an iron-sulphate catalyst supported on coke for the hydrocracking of oils.